1. Field of the Invention
The present invention relates to field effect semiconductor devices, and more particularly, to field effect semiconductor devices having trench gates.
2. Background Information
Field effect semiconductor devices having their gate electrodes disposed on the major surface of the semiconductor body have been known for many years. More recently, with the advent of reactive ion etching (RIE), the fabrication of trench gate devices has become feasible because of the ability to etch trenches having substantially vertical walls. Trench gate devices are fabricated by etching a trench in the semiconductor body through the body region of the field effect semiconductor device, growing a gate oxide on the walls of the trench and refilling the trench with polycrystalline silicon as the conductive portion of the gate electrode. Such structures can suffer from several problems. First, if the gate oxide is grown directly on the as etched trench structure, the damage to the surface silicon material resulting from the RIE etching results in many surface states at the gate oxide/silicon interface with the result that a poor field effect device results. Further, for high voltage devices (greater than about 10 volts), the sharp corner of the bottom of the trench combined with the thin gate oxide can lead to device breakdown at the corner of the trench.
Consequently, an improved technique for fabricating such devices is desirable.